This invention relates to the field of hearing aids, and more specifically, to hearing aid nubbins and acoustic dampers for eliminating resonance and improving tonal qualities in the transmission of sound between the ear and an amplifier of a hearing aid.
Many people rely upon electronic hearing aids in which sound is received by a microphone and electronically amplified to an increased volume. The amplified sound is then directed to the ear, often through a hollow sound transmission tube. Such a tube normally comprises a flexible and pliable conduit, often constructed of plastic, the hollow center of which acts as an acoustically insulated guide to direct sound vibrations from the amplifier to the ear. This is an especially common arrangement for "behind the ear," "eyeglass frame," and "in the ear" hearing aids. The sound transmission tubing provides an effective yet simple means of transmitting high quality sound to the ear.
Hearing aids of the kind described above generally have six elements: a microphone; an amplifier; a receiver; a case for the foregoing; an earpiece; and a sound transmission tube as described, between the receiver and earpiece. Additionally, hearing aids of eyeglass frame type often have a piece for intersecting and supporting the sound transmission tube known as a "nubbin." Hearing aids of behind the ear type often have a "hook," similar to a nubbin. The nubbin or hook, generically called a sound outlet port is intended to provide a precisely constructed and insulated sound channel, from one internal portion of the sound transmission tube within the case, to another, external, portion of the sound transmission tube. It also is intended to provide support upon the case than minimizes extraneous noise such as vibration.
Performance of such a hearing aid system can be drastically reduced by the presence of resonance in the nubbin or hook and sound transmission tubing. Resonance--the occurence of fixed or standing sound waves in the tubing at specific frequencies--produces distorted sound and unnatural tonal qualities. Resonance can occur at a variety of sound frequencies and result from many different sources. Hearing aids are therefore often designed to minimize resonance in the nubbin or hook and sound transmission tubing by "breaking up" or splitting the sound waves, usually by placing an obstacle such as a plug inside the tubing. Such an element mutes the distorted sound from resonance by disrupting the flow of sound waves in the tubing, thereby preventing the build-up of resonant waves. Blocking plugs or other elements in the sound concuit are referred to as "dampers," due to their ability to dampen or mute the distortion and tonal modification created by resonance.
The structure of nubbins or hooks includes several features that make them appropriate locations for dampers. Nubbins are often designed to include an interface with the sound tubing comprising a tubular protuberance with a head portion adapted to allow flexible tubing to be easily attached to the nubbin by stretching the sound tube end slightly over the protuberance. The sound channel within the nubbin extends from the end of the protuberance. A damper placed in a nubbin may be constructed of a plug with grooves in its sides. A damper like this is shown in U.S. Pat. No. 4,296,829. The plug breaks up the flow of sound waves, thereby preventing the formation of resonant waves, while the grooves allow the sound to flow past the damper to the sound transmission tubing, and eventually to the ear. A prior art grooved damper therefore consists of a plug sized to slip within a nubbin, and containing several external grooves running longitudinally along the plug surface, parallel to the nubbin sound conduit, and arranged radially about the plug sides. While useful, this damper has drawbacks. First, removal of the damper for replacement or cleaning requires disassembly of the nubbin from the case. Additionally, removal of the damper with the fingers is difficult or impossible because its small size, sung fit and location within the nubbin provide nothing for the fingers to grasp. The damper can only be removed from the nubbin after disassembly of the hearing aid case, and then only be inserting a flexible rod or wire into the opposite end of the nubbin to push the damper out. For replacement or cleaning of the damper, the nubbin must be shaped to allow insertion of the rod or wire.